The present invention is related to the field of protection switching in data communications networks.
Many data communications networks employ some form of protection switching to provide better availability of communications services to customers than can be provided by unprotected networks. Generally, protection switching involves the detection of failures within the network, the communication of the failure information to nodes that are affected by a detected failure, and the switching of traffic from one path or connection to another path or connection at the affected nodes as dictated by a predetermined protection switching scheme.
In so-called connection-oriented networks, which employ pre-established virtual and/or physical connections for carrying user data traffic, one class of protection switching schemes is known as “line-based” protection switching. In contrast to source-based schemes, in which traffic is re-routed at its source upon occurrence of a failure and may take a completely different path to its destination, line-based schemes involve more local or hop-by-hop protection switching decisions. Thus, if an end-to-end connection includes a number of intermediate nodes and connection segments and line-based protection switching is utilized, one or more of the intermediate nodes respond to a failure by taking local actions to re-route the traffic around the failure, without necessarily involving either the source or destination in the protection action. Line-based protection switching can reduce the disruption that can be caused by failures, and under some circumstances may be faster and more efficient than source-based protection switching.
Common examples of both source-based and line-based protection schemes are found in Synchronous Optical Network (SONET) networks. A SONET ring can employ unidirectional path switched ring (UPSR) protection switching or bidirectional line-switched ring (BLSR) protection switching. In UPSR protection switching, information about a failure must be propagated to the destination node, which responds by switching to accept data already flowing on a protect path separate from the working path. However, the destination node may be many hops away from the failure, potentially resulting in a long switchover delay and concomitant loss of data. In BLSR protection switching, the failure information must be propagated to every node on the ring to enable affected traffic to be re-routed in the opposite direction from source to destination, and then each node must perform the necessary switching. In either case, protection switching may be undesirably slow and/or inefficient. Additionally, these techniques suffer relatively poor scalability due to their reliance on relatively wide-area communication of failures and initiation of protection switching actions.
A protection switching technique having improved speed, efficiency and scalability is desirable.